It has long been well known to produce a soft foam article having a cover integrally adhered thereto by providing a permeable cover fabric in the shape of desired final article and pouring into the shaped cover fabric a soft polyurethane stock material to form a body foam which is integrally adhered with the cover fabric. However, if the liquid stock material is injected directly onto the inside surface of the permeable fabric, the material easily permeates into or even through the texture of the fabric so as to form disadvantageously partially stiffened areas uncomfortable in touch and called, e.g., hard spots or hard layers in the fabric. To avoid these disadvantages, it is proposed in the art to provide a buffer layer to prevent the stock solution from penetrating the cover fabric.
According to this proposal, it is alleged that a thin urethane foam (called "slab foam" or "slab urethane") is adhered as a buffer layer to the inside surface of the cover fabric. Polyurethane stock solution may be directly poured onto this urethane foam and penetrates only slightly into the urethane foam thereby to produce a thin "superficial" layer which provides sufficient bonding strength between polyurethane body foam and the cover fabric to which the slab urethane is adhered.
However, many disadvantages are found in that creamy polyurethane stock poured directly onto the slab urethane buffer layer tends to easily penetrate relatively large cells of the buffer layer or pass through the buffer layer to reach the cover fabric to adversely form thereat hard spots, or the poured stock material permeates the buffer layer over the wide range thereof to produce undesirable thick stiffened or impregnated layers.
On the other hand, for the purpose of avoiding penetration or impregnation of the body foam into the cover fabric, techniques to apply an airtight film on the inside surface of the cover fabric are proposed in various United States Patents. For example, U.S. Pat. Nos. 4,247,347 to Lischer et al., Jan. 27, 1981, 4,247,348 to Lischer, Jan. 27, 1981, 4,264,386 to Sears, Jr. et al., Apr. 28, 1981, and 4,287,143 to Sears, Jr. et al., Sep. 1, 1981 disclose applying of airtight films, preferably polyvinylchloride film, to the back surface of the cover fabric. Such airtight or impermeable films, however, deprive the finished foamed article of the permeability and leads to an uncomfortable feeling, such as a moist or sticky touch on the surface of the article.
If the use of thin urethane foam (called slab urethane) above-mentioned and the use of impermeable films taught by various U.S. Patents are combined, no particular effects can be expected to attain comfortable feelings on the surface of the article resulting from the permeability of the cover fabric. To attain the desired comfort, there must be an intermediate layer, which is permeable in nature, between the cover fabric and the body foam that also contributes to prevention of substantial penetration or :impregnation of the body foam into the intermediate layer itself.
Furthermore, use of the slab urethane as a buffer layer in the prior art is not found to be a favorable technique in that it involves time-consuming manufacturing processes such as producing first a large mass of foamed urethane and then slicing the mass into a plurality of slabs which are difficult to handle and require large space for storing them before using the same. Further, sliced slab urethane should be applied to the cover fabric by using the flame welding technique which inevitably produces a large amount of poisonous gases imparting adverse influences to workmen in the factory and also the environment thereof. In addition, if, on the basis of teachings of the aforementioned U.S. Patents, an improved method be devised wherein non-airtight, porous films can be applied to the inner surface of the aforementioned slab urethane buffer of the prior art to produce a favorably permeable foamed article, such as seat cushions, such a method cannot solve essential problems so long as it involves a cumbersome and expensive processes for preparing slab urethane foams and applying the same onto the back surface of the fabric. Further, such a method releases a large amount of poisonous gases during bonding of the film onto the buffer layer and the buffer layer onto the fabric.